I What is the minimum mass of a neutron star?

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We just discovered the maximum mass of a neutron star, discovered after the recent neutron star merger event back in Aug. They say that the maximum mass of a neutron star is approximately 2.16 solar masses.

So I always assumed that the lowest mass for one is 1.4 solar masses, the Chandresekhar Limit, but I'm not sure anymore? I'm hearing that there are neutron stars less than that size. Anyone know what the lowest theoretical limit actually is?

According to the calculations made by Oppenheimer and Volkoff in 1939, neutron stars have a theoretical mass range between 0.7 and 3.0 M⊙. Rhoades and Ruffin calculated the maximum mass of a neutron star in 1974 to be 3.2 M⊙. In 2002 Nauenberg and Chapline calculated the upper mass limit of a neutron star to be 3.6 M⊙. Since different assumptions result in different mass limits for neutron stars, it is still unknown what the actual range might be.

Some consider a theoretical lower mass limit for neutron stars smaller than the Chandrasekhar Limit to be a flaw, but as we have been recently finding out the Chandrasekhar Limit is not fixed at 1.44 M⊙ either. Depending on the density and rotational speed of the object the range limits appear to vary considerably, and there will be overlap between the maximum mass of a white dwarf and the minimum mass of a neutron star.

We just discovered the maximum mass of a neutron star, discovered after the recent neutron star merger event back in Aug. They say that the maximum mass of a neutron star is approximately 2.16 solar masses.

So I always assumed that the lowest mass for one is 1.4 solar masses, the Chandresekhar Limit, but I'm not sure anymore? I'm hearing that there are neutron stars less than that size. Anyone know what the lowest theoretical limit actually is?

No, the neutron star merger produced a black hole after a 10 to 100 milliseconds. This is the lightest BH known, not the heaviest neutron star. It establishes that the momentarily formed neutron star could not be stable, and very quickly collapsed to a BH.

We don't really know either the lowest or highest possible mass for a neutron star. It is reasonable to assume the observed mass range is statistically representative of the general population. It is unrealistic to assume electron degeneracy pressur dictates the low end because a supernova event could contirbute enough compressive force to produce degenerate stars below the Chandrasekhar mass limit, as evidenced by PSR J0453+1559. We don'yet know enough to predict a minimum mass, although it is reasonable to assume the lowest observed mass is probably in the ball park

According to the calculations made by Oppenheimer and Volkoff in 1939, neutron stars have a theoretical mass range between 0.7 and 3.0 M⊙. Rhoades and Ruffin calculated the maximum mass of a neutron star in 1974 to be 3.2 M⊙. In 2002 Nauenberg and Chapline calculated the upper mass limit of a neutron star to be 3.6 M⊙. Since different assumptions result in different mass limits for neutron stars, it is still unknown what the actual range might be.

Ah, ok. They are not saying the remnant was a 2.16 mass neutron star (consensus is that it is a ballpark 2.7 solar mass BH), but that using data from the the merger event they are able to justify this constraint. Good to know.

Actually, that should be "study," not "studies," since it was Dr. Luciano Rezzolla who wrote the one and only study which was published this month. The actual paper is provided below. What makes you think this paper is correct and everyone else is wrong?

Actually, that should be "study," not "studies," since it was Dr. Luciano Rezzolla who wrote the one and only study which was published this month. The actual paper is provided below. What makes you think this paper is correct and everyone else is wrong?

Because I read that there were other groups working independently that also came to the same conclusion, in a different article.

"This study is a good example of how theoretical and experimental research can coincide to produce better models ad predictions. A few days after the publication of their study, research groups from the USA and Japan independently confirmed the findings. Just as significantly, these research teams confirmed the studies findings using different approaches and techniques."

Ah, ok. They are not saying the remnant was a 2.16 mass neutron star (consensus is that it is a ballpark 2.7 solar mass BH), but that using data from the the merger event they are able to justify this constraint. Good to know.

Yeah, they have used the data from that merger event to tie down the upper limit completely. It's awesome that just a couple of years after the technique was perfected, Gravitational Waves are answering questions not previously answerable.

Also the final product of a 2.7 solar mass BH would probably make it the smallest known black hole yet, I suppose? I had heard the previous smallest record holder was 2.8 solar masses.

Now we need to tie down the lower limit completely too. The Oppenheimer-Volkoff limit seems to be very rough, it came up with an upper limit of 3.0 solar masses, but now we've got an actual upper limit of 2.2, so it stands to reason that the its lower limit is also pretty inaccurate.

Yeah, they have used the data from that merger event to tie down the upper limit completely. It's awesome that just a couple of years after the technique was perfected, Gravitational Waves are answering questions not previously answerable.

Also the final product of a 2.7 solar mass BH would probably make it the smallest known black hole yet, I suppose? I had heard the previous smallest record holder was 2.8 solar masses.

Now we need to tie down the lower limit completely too. The Oppenheimer-Volkoff limit seems to be very rough, it came up with an upper limit of 3.0 solar masses, but now we've got an actual upper limit of 2.2, so it stands to reason that the its lower limit is also pretty inaccurate.

Yes, the remnant is now considered the lightest known BH. I heard a talk by the lead author of the paper I linked earlier, and he said at the start we have a major record coming out of the merger - either the heaviest neutron star or the lightest BH. The question is which. He presented the work of his team, along with others to support that the result was the lightest known BH.

Yeah, they have used the data from that merger event to tie down the upper limit completely. It's awesome that just a couple of years after the technique was perfected, Gravitational Waves are answering questions not previously answerable.

Also the final product of a 2.7 solar mass BH would probably make it the smallest known black hole yet, I suppose? I had heard the previous smallest record holder was 2.8 solar masses.

Now we need to tie down the lower limit completely too. The Oppenheimer-Volkoff limit seems to be very rough, it came up with an upper limit of 3.0 solar masses, but now we've got an actual upper limit of 2.2, so it stands to reason that the its lower limit is also pretty inaccurate.

One very questionable event does not establish a standard, no matter how much you wish it to be true.

Oppenheimer and Volkoff's calculations are based upon certain assumptions about the properties of a neutron star, as are all the other estimated neutron star mass ranges. Just because you now have a different mass range based upon completely different set of assumptions does not invalidate any of the other calculations until you can show that their assumptions were incorrect.

Oppenheimer and Volkoff also calculated that the theoretical lower end for a neutron star was 0.7 M⊙ and we know of at least one neutron star that is below the Chandrasekhar Limit. Considering white dwarfs and neutron stars are cores of dead stars that came about as a result of two completely different processes, it makes sense that one would have absolutely nothing to do with the other. A white dwarf does not become a neutron star as soon as they exceed 1.44 M⊙, nor does a neutron star cease to be just because it is below the Chandrasekhar Limit.

Keep in mind that the Chandrasekhar Limit is also based upon certain assumptions. We have observed both sub- and super-Chandrasekhar Limit Type Ia SN, so those Chandrasekhar Limit assumptions are not the only thing that produce Type Ia SN. The same is undoubtedly true for neutron stars. Be wary of locking in on just one particular assumption and assuming that only it can be true and everything else must be false.

Or possibly a neutron core that either ejected part of its core during the deflagration, or lost some mass as a result of a collision, resulting in a mass smaller than the Chandrasekhar Limit. After all, it is the density that determines a neutron star, not its mass.

Oppenheimer and Volkoff's calculations are based upon certain assumptions about the properties of a neutron star, as are all the other estimated neutron star mass ranges. Just because you now have a different mass range based upon completely different set of assumptions does not invalidate any of the other calculations until you can show that their assumptions were incorrect.

Oppenheimer and Volkoff also calculated that the theoretical lower end for a neutron star was 0.7 M⊙ and we know of at least one neutron star that is below the Chandrasekhar Limit. Considering white dwarfs and neutron stars are cores of dead stars that came about as a result of two completely different processes, it makes sense that one would have absolutely nothing to do with the other. A white dwarf does not become a neutron star as soon as they exceed 1.44 M⊙, nor does a neutron star cease to be just because it is below the Chandrasekhar Limit.

Keep in mind that the Chandrasekhar Limit is also based upon certain assumptions. We have observed both sub- and super-Chandrasekhar Limit Type Ia SN, so those Chandrasekhar Limit assumptions are not the only thing that produce Type Ia SN. The same is undoubtedly true for neutron stars. Be wary of locking in on just one particular assumption and assuming that only it can be true and everything else must be false.

As a result of these superluminous Type Ia SN discoveries being made since 2003 there have been new assumptions made about white dwarfs. Some place the new limit at almost double the Chadrasekhar Limit, at 2.58 M⊙. While others have suggested that magnetic fields may result in superluminous Type Ia SN that exceed the Chadrasekhar Limit.

As a result of these superluminous Type Ia SN discoveries being made since 2003 there have been new assumptions made about white dwarfs. Some place the new limit at more than double the Chadrasekhar Limit, at 2.58 M⊙. While others have suggested that magnetic fields may result in superluminous Type Ia SN that exceed the Chadrasekhar Limit.

Thanks, I had been thinking of white dwarfs we have observed directly, for which I still see no sign of overmass dwarf. However, the inference of overmass dwarfs from events these papers analyze is, admittedly, quite convincing.

Ok, the really interesting question about these inferred overmass dwarfs is the possibility you may have a white dwarf more massive than the lightest BH; the inferred masses are already well over the heaviest ever observed neutron star.

I'm looking for a paper I can cite that gives a lower credible limit for a neutron star mass, specifically to rule out an NS being below 0.5 Msun which I think should be possible. Do you have a specific source for your statement, it would be very helpful.